Systems and methods for delivering sub-threshold therapy to a patient at a physiological midline

Abstract

A method of operating an implantable neuromodulator coupled to an electrode array implanted adjacent tissue of a patient includes conveying electrical modulation energy to the tissue per a series of modulation parameter sets, thereby displacing the locus of the resulting electrical field laterally relative to the tissue, associating a plurality of different loci with the modulation parameter sets, causing the patient to perceive paresthesia, identifying a modulation parameter set as creating an electrical field having a locus disposed on a physiological midline of the patient based on the perceived paresthesia, deriving another modulation parameter set from the identified modulation parameter set, conveying electrical modulation energy to the patient per the other modulation parameter set, thereby creating an electrical field having a locus relative to the tissue that is the same as the locus of the electrical field associated with the identified modulation parameter set, without causing paresthesia.

What is claimed is: 
     
       1. A method of operating an implantable neuromodulator coupled to an electrode array implanted adjacent tissue of a patient having a medical condition, comprising:
 conveying electrical modulation energy to the patient's tissue in accordance with a series of modulation parameter sets, thereby gradually displacing a locus of a resulting electrical field laterally relative to the tissue, such that a plurality of different loci of the resulting electrical field can be respectively associated with the series of modulation parameter sets; 
 causing the patient to perceive paresthesia in response to the conveyance of the electrical modulation energy to the tissue in accordance with at least one of the modulation parameter sets; 
 identifying one of the at least one modulation parameter sets as creating an electrical field having another locus disposed on a physiological midline of the patient based on the perceived paresthesia; 
 deriving another modulation parameter set from the identified modulation parameter set; 
 conveying electrical modulation energy to the patient's tissue in accordance with the other modulation parameter sets, thereby creating an electrical field having a new locus relative to the tissue that is the same as the locus of the electrical field associated with the identified modulation parameter set, and without causing the patient to perceive paresthesia. 
 
     
     
       2. The method of  claim 1 , wherein the medical condition affects a body region of the patient, the electrical modulation energy conveyed to the tissue in accordance with the identified modulation parameter set causes the patient to perceive the paresthesia in the body region. 
     
     
       3. The method of  claim 1 , wherein the medical condition is chronic pain. 
     
     
       4. The method of  claim 1 , wherein the identified modulation parameter set and the other modulation parameter set define different pulse rates. 
     
     
       5. The method of  claim 4 , wherein the identified modulation parameter set defines a pulse rate less than 1500 Hz, and the other modulation parameter set defines a pulse rate greater than 1500 Hz. 
     
     
       6. The method of  claim 1 , wherein the identified modulation parameter set and the other modulation parameter set define different pulse widths. 
     
     
       7. The method of  claim 6 , wherein the identified modulation parameter set defines a pulse width greater than 100 μs, and the other modulation parameter set defines a pulse width less than 100 μs. 
     
     
       8. The method of  claim 1 , wherein the identified modulation parameter set defines an electrode combination, and wherein the other modulation parameter set defines the same electrode combination. 
     
     
       9. The method of  claim 8 , wherein the electrode combination comprises a fractionalized electrode combination. 
     
     
       10. The method of  claim 8 , wherein the electrode combination comprises a multipolar electrode combination. 
     
     
       11. The method of  claim 1 , further comprising:
 displacing a virtual pole relative to the electrode array; and 
 computing fractionalized electrode combinations that respectively emulate the displaced virtual pole, wherein the series of modulation parameter sets respectively define the fractionalized electrode combinations, 
 wherein the identified modulation parameter set defines a fractionalized electrode combination corresponding to one of the series of virtual poles, and 
 wherein the other modulation parameter set defines the same fractionalized electrode combination. 
 
     
     
       12. The method of  claim 11 , wherein the virtual pole is laterally displaced across the electrode array. 
     
     
       13. The method of  claim 1 , further comprising programming the neuromodulator with the other modulation parameter set. 
     
     
       14. The method of  claim 1 , wherein the neuromodulator is implanted within the patient. 
     
     
       15. The method of  claim 1 , wherein the tissue is spinal cord tissue. 
     
     
       16. The method of  claim 1 , further comprising displacing the locus of the resulting electrical field relative to the tissue in response to user input. 
     
     
       17. A method of providing therapy to a patient using an implantable neuromodulator implanted within the patient, comprising:
 conveying electrical modulation energy to tissue of the patient to generate an electrical field having a locus relative to the tissue in a super-threshold mode, thereby causing the patient to perceive paresthesia; 
 laterally steering the locus of the electrical field by modifying a fractionalized electrode combination while operating the neuromodulator in the super-threshold delivery mode and receiving feedback from the patient to determine a physiological midpoint; 
 identifying a locus disposed on a physiological midline of the patient and a corresponding fractionalized electrode combination based on the perceived paresthesia; 
 switching operation of the neuromodulator to the a sub-threshold delivery mode, while maintaining corresponding fractionalized electrode combination; and 
 delivering electrical modulation energy to the identified locus on the physiological midline of the patient in the sub-threshold delivery mode to provide sub-threshold therapy to the patient, 
 wherein the neuromodulator delivers electrical modulation energy to the patient when in the sub-threshold delivery mode that provides sub-threshold therapy to the patient. 
 
     
     
       18. The method of  claim 17 , further comprising:
 identifying another locus disposed on the physiological midline of the patient and another corresponding fractionalized electrode combination based on the perceived paresthesia; and 
 delivering electrical modulation energy to the other identified locus on the physiological midline of the patient in the sub-threshold delivery mode to provide sub-threshold therapy to the patient. 
 
     
     
       19. The method of  claim 17 ; further comprising identifying a plurality of loci disposed on the physiological midline of the patient and a plurality of corresponding fractionalized electrode combination based on the perceived paresthesia;
 fitting a curve to the plurality of loci disposed on the physiological midline; 
 switching operation of the neuromodulator to the a sub-threshold delivery mode; and 
 delivering electrical modulation energy to a point on the fitted curve of the patient in the sub-threshold delivery mode to provide sub-threshold therapy to the patient, 
 wherein the neuromodulator delivers electrical modulation energy to the patient when in the sub-threshold delivery mode that provides sub-threshold therapy to the patient. 
 
     
     
       20. The method of  claim 17 , wherein:
 the neuromodulator delivers the electrical modulation energy at a pulse rate less than 1500 Hz when in the super-threshold delivery mode, and delivers the electrical modulation energy at a pulse rate greater than 1500 Hz when in the sub-threshold delivery mode; or 
 the neuromodulator delivers the electrical modulation energy at a pulse width greater than 100 us when in the super-threshold delivery mode, and delivers the electrical modulation energy at a pulse width less than 100 μs when in the sub-threshold delivery mode; or 
 the neuromodulator delivers the electrical modulation energy at a pulse width greater than 200 μs when in the super-threshold delivery mode, and delivers the electrical modulation energy at a pulse width less than 50 μs when in the sub-threshold delivery mode.